Structure and methodology for fabrication and inspection of photomasks

ABSTRACT

A photomask, method of designing, of fabricating, of designing, a method of inspecting and a system for designing the photomask. The photomask, includes: a cell region, the cell region comprising one or more chip regions, each chip region comprising a pattern of opaque and clear sub-regions corresponding to features of an integrated circuit chip and one or more kerf regions, each kerf region comprising a pattern of opaque and clear sub-regions corresponding to features of an integrated circuit kerf; a clear region formed adjacent to a side of a copy region, the copy region comprising opaque and clear sub-regions that are copies of at least a part of the cell region; and an opaque region between the clear region and the cell region.

RELATED APPLICATIONS

This Application is a division of co-pending application Ser. No.10/908,284.

FIELD OF THE INVENTION

The present invention relates to the field of photomasks; morespecifically, it relates to structures for photomasks and methodologiesfor fabrication and inspection of photomasks.

BACKGROUND OF THE INVENTION

As the density of integrated circuit chips increase and the physicalimage sizes decrease, defect inspection of the photomasks used tofabricate integrated circuit chips has become ever more important. Theseimages have become far too small and numerous for human visualinspection and verification. Therefore machine inspection methods havedeveloped. However, there are regions on photomasks that are printed onwafers during manufacture of integrated circuit chips that repeat andother regions that do not repeat. Inspection of repeating images and ofnon-repeating images require different machine methods of inspection.Implementing two machine methods in a mask manufacturing facility can beexpensive and time consuming.

Therefore, there is a need for a single machine methodology forinspecting photomasks having regions that repeat and regions that do notrepeat.

SUMMARY OF THE INVENTION

The present invention places copies of clear and opaque regions withinthe cell region of a photomask within clear bar regions of thephotomask. The clear bars are disposed within an opaque frame thatsurrounds the cell region. The copies clear and opaque regions can thenbe compared to the corresponding clear and opaque regions in the cellregion.

A first aspect of the present invention is a photomask, comprising: acell region, the cell region comprising one or more chip regions, eachchip region comprising a pattern of opaque and clear sub-regionscorresponding to features of an integrated circuit chip and one or morekerf regions, each kerf region comprising a pattern of opaque and clearsub-regions corresponding to features of an integrated circuit kerf; aclear region formed adjacent to a side of a copy region, the copy regioncomprising opaque and clear sub-regions that are copies of at least apart of the cell region; and an opaque region between the clear regionand the cell region.

A second aspect of the present invention is a method of inspecting aphotomask, comprising: providing the photomask, the photomaskcomprising: a cell region, the cell region comprising one or more chipregions, each chip region comprising a pattern of opaque and clearsub-regions corresponding to features of an integrated circuit chip andone or more kerf regions, each kerf region comprising a pattern ofopaque and clear sub-regions corresponding to features of an integratedcircuit kerf; a clear region formed adjacent to a side of a copy region,the copy region comprising opaque and clear sub-regions that are copiesof at least a part of the cell region; and an opaque region between theclear region and the cell region; performing an image scan of the copyregion; performing an image scan of a portion of the cell regioncorresponding to the copy region; performing a comparison comprising acomparing of the image scan of the copy region and the image scan of thecorresponding portion of the cell region; and

determining locations of potential defects in the corresponding portionof the cell region based on the comparison or both determining thelocations of potential defects in the corresponding portion of the cellregion and determining corresponding locations of potential defects inthe copy region based on the comparison.

A third aspect of the present invention is a method of designing aphotomask, comprising: generating a chip dataset representing anintegrated circuit chip design to be included in a cell region of thephotomask; generating a kerf dataset representing a kerf design to beincluded in the cell region; determining a portion of the kerf datasetto copy; generating a kerf copy dataset, the kerf copy dataset includingthe portion of the kerf dataset to copy; merging the chip dataset, thekerf dataset and the kerf copy dataset into a photomask datasetrepresenting a pattern of clear and opaque regions of the photomask.

A fourth aspect of the present invention is a computer system comprisinga processor, an address/data bus coupled to the processor, and acomputer-readable memory unit coupled to communicate with the processor,the memory unit containing instructions that when executed implement amethod for method of designing a photomask, the method comprising thecomputer implemented steps of: generating a chip dataset representing anintegrated circuit chip design to be included in a cell region of thephotomask; generating a kerf dataset representing a kerf design to beincluded in the cell region; determining a portion of the kerf datasetto copy; generating a kerf copy dataset, the kerf copy dataset includingthe portion of the kerf dataset to copy; merging the chip dataset, thekerf dataset and the kerf copy dataset into a photomask datasetrepresenting a pattern of clear and opaque regions of the photomask.

A fifth aspect of the present invention is a method of fabricating aphotomask, comprising: providing a transparent substrate having anopaque coating; forming a cell region by removing first areas of theopaque coating, the cell region comprising one or more chip regions andone or more kerf regions; forming a copy region by removing second areasof the opaque coating, the copy region comprising a copy of a part ofthe cell region; forming a clear region by completely removing thirdareas of the opaque coating; and wherein the clear region is formedbetween a side of the substrate and a side of the cell region andseparated from the cell region by an opaque region and wherein asub-region of the clear region separates the copy region from the opaqueregion.

BRIEF DESCRIPTION OF DRAWINGS

The features of the invention are set forth in the appended claims. Theinvention itself, however, will be best understood by reference to thefollowing detailed description of an illustrative embodiment when readin conjunction with the accompanying drawings, wherein:

FIG. 1 is a top view of an exemplary photomask illustrating a firstembodiment of the present invention;

FIG. 2 is a top view of an exemplary photomask illustrating a secondembodiment of the present invention;

FIG. 3 is a top view of an exemplary photomask illustrating a thirdembodiment of the present invention;

FIG. 4 is a top view of an exemplary photomask illustrating cording afourth embodiment of the present invention;

FIG. 5 is a top view of an exemplary photomask illustrating a fifthembodiment of the present invention;

FIG. 6 is a flowchart illustrating a method of inspecting a photomaskaccording to the present invention;

FIG. 7 is a flowchart of a method of designing a photomask according tothe present invention; and

FIG. 8 is a schematic block diagram of a general-purpose computer foruse in designing a photomask according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is applicable to conventional photomasksfabricated from a transparent substrate, for example glass, quartz, orother materials on which a opaque layer has been formed, for example alayer of chrome or a dual layer of chrome over molybdenum. The presentinvention is also applicable to phase shift masks in which notches havebeen formed to thin the transparent substrate are immediately adjacentto the edges of opaque features. The present invention is furtherapplicable to “chromeless” masks having no “opaque” coating but ratherregions of the substrate with zero radian phase shifts and regions of πor −π in phase shifts. It should be understood that the phase shift of alayer is a function of thickness and that the intensity ofelectromagnetic radiation passing through a layer is proportional to thesecond power of the phase (in radians).

For conventional photomasks, clear regions are formed by removal of theopaque layer by a photolithographic process. In one example, aphotoresist layer is applied to mask blank (a transparent substratehaving a continuous opaque layer), a pattern is exposed into thephotoresist by a mask-writing tool, such as an electron beam tool drivenby a dataset (described infra), the photoresist developed, the opaquelayer etched away (for example by a reactive ion etch process) where itis exposed by the development process and then the remaining photoresistlayer removed leaving a patterned region which comprises opaquesub-regions and clear areas sub-regions.

For phase shift, or other advanced types of masks, an additionalphotolithographic process may be used form the notches in the“transparent” substrate. For “chromeless” phase shift masks a singlephotolithographic process may be used form a pattern of thin and thickregions in the “transparent” substrate

It should be understood that the term transparent means light of thewavelength used by the exposure tool using the photomask in a integratedcircuit chip manufacturing line will pass through the substrateun-attenuated to the degree that a positive photoresist layer on a waferin the exposure tool will be exposed sufficiently to be removed by achemical development process. Clear regions are thus transparent. Opaqueregions will attenuate or completely block light of the wavelength usedby the exposure tool using the photomask in a integrated circuit chipmanufacturing line to the degree that a positive photoresist layer on awafer in the exposure tool will not be exposed sufficiently to beremoved by the development process. A positive photoresist is aphotoresist that is de-polymerized when exposed to actinic radiation.

By these definitions all masks have clear and opaque regions.

It should be further understood, that a photomask contains a cell regioncomprising one or more chip regions and one or more kerf regions. Thechip regions are comprised of a pattern of opaque and clear sub-regionscorresponding to features of an integrated circuit chip (at a particularlevel of build of the integrated circuit chip). Each kerf region iscomprised of a pattern of opaque and clear sub-regions corresponding tofeatures of an integrated circuit kerf chip (at the particular level ofbuild of the integrated circuit chip).

Kerfs comprise a dicing channel filled with structures that are used forphysical and/or electrical image measurements, device parametricmeasurements and alignment marks (images that allow a current mask to bealigned to pattern on the wafer formed by an earlier used mask),alignment measurement structures, and other non-chip integrated circuitchip structures. Kerfs are also known in the art as streets or scribelines.

In a photolithographic process of an integrated circuit manufacturingline, the pattern of opaque and clear sub-regions of the cell regionwill be transferred into a photoresist layer on a semiconductor waferduring fabrication of a level of an integrated circuit chip.

FIG. 1 is a top view of an exemplary photomask illustrating a firstembodiment of the present invention. In FIG. 1, a rectangular photomask100 has opposing parallel first second sides 105A and 105B and opposingparallel third and fourth sides 105C and 105D. Photomask 100 includes acell region 110 and an opaque frame region 115 completely surrounding arectangular cell region 110. Cell region 110 has opposing parallel firstand second sides 120A and 120B and opposing parallel third and fourthsides 120C and 120D. First, second, third and fourth sides 105A, 105B,105C and 105D of photomask 100 are parallel to first, second, third andfourth sides 120A, 120B, 120C and 120D of cell region 110 respectively.

Disposed between first side 105A of photomask 100 and first side 120A ofcell region 110 and contained completely within frame region 115 is afirst rectangular clear region, hereafter first clear bar 125A. Firstclear bar 125A has a length measured in a direction parallel to firstside 120A of cell region 110 that is longer than a length of first side120A of cell region 110. A first end 130A of first clear bar 125Aextends past a first corner 135A of cell region 110 formed by theintersection of first and third sides 120A and 120C of cell region 110.A second end 130B of first clear bar 125A extends past a second corner135B of cell region 110 formed by the intersection of first and fourthsides 120A and 120D of cell region 110.

Disposed between second side 105B of photomask 100 and second side 120Bof cell region 110 and contained completely within frame region 115 is asecond rectangular clear region, hereafter second clear bar 125B. Secondclear bar 125B has a length measured in a direction parallel to secondside 120B of cell region 110 that is longer than a length of second side120B of cell region 110. A first end 140A of second clear bar 125Bextends past a third corner 135C of cell region 110 formed by theintersection of second and third sides 120B and 120C of cell region 110.A second end 140B of second clear bar 125B extends past a fourth comer135D of cell region 110 formed by the intersection of second and fourthsides 120B and 120D of cell region 110.

Disposed between third side 105C of photomask 100 and third side 120C ofcell region 110 and contained completely within frame region 115 is athird rectangular clear region, hereafter third clear bar 125C. Thirdclear bar 125C has a length measured in a direction parallel to thirdside 120C of cell region 110 that is longer than a length of third side120C of cell region 110. A first end 145A of third clear bar 125Cextends past third corner 135C of cell region 110. A second end 145B ofthird clear bar 125B extends past first corner 135A of cell region 110.

Disposed between fourth side 105D of photomask 100 and fourth side 120Dof cell region 110 and contained completely within frame region 115 is afourth rectangular clear region, hereafter fourth clear bar 125D. Fourthclear bar 125D has a length measured in a direction parallel to fourthside 120D of cell region 110 that is longer than a length of fourth side120D of cell region 110. A first end 150A of fourth clear bar 125Dextends past fourth corner 135D of cell region 110. A second end 150B offourth clear bar 125D extends past second corner 135B of cell region110.

Cell region 110 includes first, second, third and fourth chip (or die)regions 155A, 155B, 155C and 155D, first, second, third and fourthinterstitial kerf regions 160A, 160B, 160C and 160D and first and secondperipheral kerf regions 165A and 165B. First, second, third and fourthchip regions 155A, 155B, 155C and 155D, first, second, third and fourthinterstitial kerf regions 160A, 160B, 160C and 160D and first and secondperipheral kerf regions 165A and 165B are each comprised of a pattern ofopaque and transparent regions. Interstitial kerfs are kerf regions thatare disposed between two different chip regions and peripheral kerfregions are kerf regions disposed between a chip region and an side of acell region.

In a photolithographic process of an integrated circuit manufacturingline, first, second, third and fourth chip regions 155A, 155B, 155C and155D and first, second, third and fourth interstitial kerf regions 160A,160B, 160C and 160D and first and second peripheral kerf regions 165Aand 165B will define the various images formed in a photoresist layer ona semiconductor wafer for a fabrication level of integrated circuitchip.

First clear bar 125A contains a first and a second interstitial kerfcopy regions 170A and 170B. First interstitial kerf copy region 170Aincludes all the patterns of first interstitial kerf region 160A plus anextension 175A which includes at least portions of those patterns fromadjacent regions of third and fourth first interstitial kerf regions160C and 160D that extend into first interstitial kerf region 160A.Second interstitial kerf copy region 170B includes all the patterns ofsecond interstitial kerf region 160B plus a first extension 175B whichincludes at least portions of those patterns from adjacent regions ofthird and fourth interstitial kerf regions 160C and 160D that extendinto second interstitial kerf region 160B and a second extension 175Cwhich includes at least portions of those patterns from adjacent regionsof first peripheral kerf region 165A that extend into secondinterstitial kerf region 160B. It should be noted that first and asecond interstitial kerf copy regions 170A and 170B are located withinfirst clear bar 125A so there is always a continuous clear band of firstclear bar 125A containing no opaque shapes surrounding interstitial kerfcopy regions 170A and 170B.

Third clear bar 125C contains a third and a fourth interstitial kerfcopy regions 170C and 170D. Third interstitial kerf copy region 170Ccontains all the patterns of first interstitial kerf region 160C plus anextension 175D which includes at least portions of those patterns fromadjacent regions of fourth interstitial kerf region 160D that extendinto first interstitial kerf region 160C. Fourth interstitial kerf copyregion 170D includes all the patterns of fourth interstitial kerf region160D plus a first extension 175E which includes at least portions ofthose patterns from adjacent regions of third interstitial kerf region160C that extend into second interstitial kerf region 160B and a secondextension 175FC which includes at least portions of those patterns fromadjacent regions of second peripheral kerf region 165B that extend intofourth interstitial kerf region 160D. It should be noted that third anda fourth interstitial kerf copy regions 170C and 170D are located withinthird clear bar 125C so there is always a continuous clear band of firstclear bar 125C containing no opaque shapes surrounding interstitial kerfcopy regions 170C and 170D.

Fourth clear bar 125D contains a first peripheral kerf copy region 180A.First peripheral kerf copy region 180A includes all the patterns offirst peripheral kerf region 165A plus a first extension 185A whichincludes at least portions of those patterns from adjacent regions ofsecond interstitial kerf region 160B that extend into first peripheralkerf region 165A and a second extension 185B which includes at leastportions of those patterns from adjacent regions of second peripheralkerf region 165B that extend into first peripheral kerf region 165B. Itshould be noted that first peripheral kerf copy region 180A is locatedwithin fourth clear bar 125D so there is always a continuous clear bandof fourth clear bar 125D containing no opaque shapes surrounding firstperipheral kerf copy region 180A.

Second clear bar 125B contains a second peripheral kerf copy region180B. Second peripheral kerf copy region 180B includes all the patternsof second peripheral kerf region 165B plus a first extension 185C whichincludes at least portions of those patterns from adjacent regions offourth interstitial kerf region 160DB that extend into second peripheralkerf region 165B and a second extension 185D which includes at leastportions of those patterns from adjacent regions of first peripheralkerf region 165A that extend into second peripheral kerf region 165B. Itshould be noted that second peripheral kerf copy region 180B is locatedwithin second clear bar 125B so there is always a continuous clear bandof second clear bar 125B containing no opaque shapes surrounding secondperipheral kerf copy region 180B.

It has been noted that there is a continuous clear band of clear barsurrounds any copy regions within the clear bar. One use of clear barsis to modify the abrupt transition from the cell region which can be,for example 70% clear area and 30% opaque area to the frame which is100% opaque area. With clear bars, the transition becomes, for example,from 70% clear area and 30% opaque area to 100% opaque area to 100%clear area which has the effect of improving image size control duringthe photomask manufacturing process. There is a minimum width W of thiscontinuous clear band below which, while the present invention isoperable, the beneficial effect on image size control during photomaskmanufacture is lost.

In a photolithographic process of an integrated circuit manufacturingline, the patterns of first, second, third and fourth interstitial kerfcopy regions 170A, 170B, 170C and 170D and first and second peripheralkerf copy regions 180A and 180B not will be transferred to a wafer.Shutter blades of the photolithographic exposure tool of the integratedcircuit chip manufacturing line will cover all of clear bars 125A, 125B,125C and 125D. The shutter blades will overlap regions of the opaqueframe 115 between cell region 110 and clear bars 125A, 125B, 125C and125D.

In one example, chip regions 155A, 155B, 155C and 155D have identicalclear and opaque patterns, i. e. are identical designs. In a secondexample, a first pair of two of chip regions 155A, 155B, 155C and 155Dare identical to each other and a second pair having different chipregions from the first pair are identical to each other.

By having sets of chips that identical, machine defect inspection ofchip regions by comparison of scanned image data from each chip regioncan be performed. By having interstitial kerf regions and copies of theinterstitial kerf regions (located in the clear bars), machine defectinspection by comparison of scanned image data from each uniqueinterstitial kerf region can be compared to scanned image data of acorresponding copy (as illustrated in FIG. 6 and described infra).Similarly, by having peripheral kerf regions and copies of theperipheral kerf regions (located in the clear bars), machine defectinspection by comparison of scanned image data from each uniqueperipheral kerf region can be compared to scanned image data of acorresponding copy (as illustrated in FIG. 6 and described infra). Itshould be understood, that a potential defect is flagged when thescanned image data from corresponding regions of different but identicalstructures do not match.

It should also be noted, that if two or more interstitial or two or moreperipheral kerfs are identical, it becomes optional to include anycopies of the non-unique interstitial peripheral kerfs in the clear barregions. However, reasons for including copies of the non-uniqueinterstitial peripheral kerfs in the clear bar regions is discussedinfra.

While four chips and six unique kerfs are illustrated in FIG. 1, thefirst embodiment of the present invention is equally applicable tophotomasks having at least a pair of identical chips and at least oneunique kerf or at the very least having at least one unique kerf.

Interstitial kerf region 160A and 160B may comprise a single kerf regionin which case adjustments to interstitial kerf copy regions 170A and170B will be required or interstitial kerf regions 160C and 160D maycomprise a single kerf region in which case adjustments to interstitialkerf copy regions 170C and 170D will be required.

The present invention allows unique kerf photomasks to be inspected bycomparing kerf scanned image data to kerf copy scanned image data.Applicants have seen about a 30% improvement in defect detectionreliability using scanned image data to scanned image data comparisonover scanned image data to dataset synthesized image data comparison.

While four individual clear bar regions have been illustrated severalother options exist. First, two adjacent clear bars may be joinedtogether in an “L” shaped configuration. Second, a first of two adjacentclear bars may be joined together in a first “L” shaped configurationand the remaining two clear bars may be joined together in a second “L”shaped configuration. Third, three clear bars may be joined together ina “U” shaped configuration. Fourth, all four clear bars may be joinedtogether in a ring shaped configuration. In all four options, acontinuous opaque will exist between the cell region of the photomaskand the clear bars.

FIG. 2 is a top view of an exemplary photomask illustrating a secondembodiment of the present invention. In FIG. 2, a photomask 100A issimilar to photomask 100 of FIG. 1, except for the following fourdifferences:

First, first clear bar 125A contains in addition to first and secondinterstitial kerf copy regions 170A and 170B, third and fourthinterstitial kerf copy regions 170AA and 170BB where third interstitialkerf copy region 170AA is identical to first interstitial kerf copyregion 170A and fourth interstitial kerf copy region 170BB is identicalto second interstitial kerf copy region 170B.

Second, second clear bar 125B contains in addition to second peripheralkerf copy region 180B a third peripheral kerf copy region 180BB wherethird peripheral kerf copy region 180BB is identical to secondperipheral kerf copy region 180B.

Third, third clear bar 125C contains in addition to first and secondinterstitial kerf copy regions 170C and 170C, third and fourthinterstitial kerf copy regions 170CC and 170DD where third interstitialkerf copy region 170CC is identical to first interstitial kerf copyregion 170C and fourth interstitial kerf copy region 170DD is identicalto second interstitial kerf copy region 170D.

Fourth, fourth clear bar 125D contains in addition to first peripheralkerf copy region 180A a fourth peripheral kerf copy region 180AA wherefourth peripheral kerf copy region 180AA is identical to firstperipheral kerf copy region 180A.

The duplicate copies of each interstitial kerf copy region and eachperipheral kerf copy region significantly increases the probability ofdetermining if a potential defect detected lies in a kerf copy region ora kerf region of the cell region. As mentioned supra, a potential defectis flagged when the data from corresponding regions of identicalstructures do not match. If there are three identical regions and onedoes not match, there is a high probability that the defect lies in theregion that does not match the other two.

While four chips and six unique kerfs are illustrated in FIG. 2, thesecond embodiment of the present invention is equally applicable tophotomasks having at least a pair of identical chips and at least oneunique kerf or at the very least having at least one unique kerf.

FIG. 3 is a top view of an exemplary photomask illustrating a thirdembodiment of the present invention. In FIG. 3, a photomask 100B issimilar to photomask 100 of FIG. 1, except for the following fourdifferences:

First, a cell region 110A includes fifth and sixth chip regions 155E and155F in addition to first, second, third and fourth chip regions 155A,155B, 155C and 155D as well as fifth, sixth and seventh interstitialkerf regions 160E, 160F and 160G in addition to first, second, third andfourth interstitial kerf regions 160A, 160B, 160C and 160D.

Second, first clear bar 125A contains in addition to first and secondinterstitial kerf copy regions 170A and 170B, fifth and seventhinterstitial kerf copy regions 170E and 170G. Fifth interstitial kerfcopy region 170E includes all the patterns of fifth interstitial kerfregion 165E plus a first extension 190A which includes at least portionsof those patterns from adjacent regions of fourth interstitial kerfregion 160D and sixth interstitial kerf region 160F that extend intofifth peripheral kerf region 165E. Seventh interstitial kerf copy region170G includes all the patterns of seventh interstitial kerf region 165Gplus a first extension 190B which includes at least portions of thosepatterns from adjacent regions of fourth interstitial kerf region 160Dand sixth interstitial kerf region 160F that extend into seventhinterstitial kerf region 160G and a second extension 190C which includesat least portions of those patterns from adjacent regions of firstperipheral kerf region 165A that extend into seventh interstitial kerfregion 160G.

Third, third clear bar 125C contains in addition to third and fourthinterstitial kerf copy regions 170C and 170D, fifth interstitial kerfcopy region 170F. Sixth interstitial kerf copy region 170F includes allthe patterns of sixth interstitial kerf region 165F plus a firstextension 190D which includes at least portions of those patterns fromadjacent regions of third interstitial kerf region 160C that extend intosixth interstitial kerf region 160F and a second extension 190E whichincludes at least portions of those patterns from adjacent regions offourth interstitial kerf region 160D that extend into sixth interstitialkerf region 160F. Additionally, third interstitial kerf copy region 170Cis modified so extension 175D includes patterns of sixth interstitialkerf region 165F (instead of fourth interstitial kerf region 160D) thatextend into sixth interstitial kerf region 160F and fourth interstitialkerf copy region 170D is modified so first extension 175E includespatterns of sixth interstitial kerf region 165F (instead of thirdinterstitial kerf region 160C) that extend into sixth interstitial kerfregion 160F.

Fourth, first peripheral kerf copy region 180A further includes a thirdextension 185C which includes at least portions of those patterns fromadjacent regions of seventh interstitial kerf region 160G that extendinto first peripheral kerf region 165A.

FIG. 4 is a top view of an exemplary photomask illustrating a fourthembodiment of the present invention. In FIG. 4, a photomask 100C issimilar to photomask 100 of FIG. 1, except for the following fourdifferences:

First, a cell region 110B includes only a single chip region 155Ginstead of four chip regions, 155A, 155B, 155C and 155D as in FIG. 1 andthere are no interstitial kerf regions. Chip region 155G is divided intofirst and second partial chip regions 195A and 195B by an axis 200parallel to side 105A of photomask 100C.

Second, first clear bar 125A contains a first partial copy region 205Ainstead of first and second interstitial kerf copy regions 170A and 170B(see FIG. 1). First partial copy region 205A includes a first partialchip copy region 210A which includes all the patterns of first partialchip region 195A, a first extension region 215A which includes at leastportions of those patterns from adjacent regions of second partial chipregion 195B that extend into first partial chip region 195A, a firstperipheral kerf copy region 220A which includes at least portions ofthose patterns from the portion of first peripheral kerf 165A adjacentto first chip partial region 195A, and a second extension region 225Awhich includes at least portions of those patterns from the portion offirst peripheral kerf 165A that overlap axis 200.

Third, second clear bar 125B contains a second partial copy region 205Binstead of second peripheral kerf copy regions 180B (see FIG. 1). Secondpartial copy region 205B includes a second partial chip copy region 210Bwhich includes all the patterns of second partial chip region 195B, afirst extension region 215B which includes at least portions of thosepatterns from adjacent regions of first partial chip region 195A thatextend into second partial chip region 195BA, a second peripheral kerfcopy region 220B which includes at least portions of those patterns fromthe portion of first peripheral kerf 165A adjacent to second chippartial region 195B, a second extension region 225B which includes atleast portions of those patterns from the portion of first peripheralkerf 165A that overlap axis 200, and third peripheral kerf copy region230 that includes all the patterns of second peripheral kerf 165B.

Fourth, clear bars 125B and 125D are empty, that is they contain noopaque regions.

The present invention allows unique kerf photomasks to be inspected bycomparing kerf scanned image data to kerf copy scanned image data.Applicants have seen about a 30% improvement in defect detectionreliability using scanned image data to scanned image data comparisonover scanned image data to dataset synthesized image data comparison.

FIG. 5 is a top view of an exemplary photomask illustrating a fifthembodiment of the present invention. In FIG. 5, a photomask 100D issimilar to photomask 100C of FIG. 5, except for the following fivedifferences:

First, chip region 155G is divided into first, second, third and fourthpartial chip regions 195A, 195B, 195C and 195D by an axes 200A, 200B and200C which are mutually parallel and parallel to side 105A of photomask100D.

Second, first extension region 215A includes at least portions of thosepatterns from adjacent regions of third partial chip region 195C (ratherthan second region 195B) that extend into first partial chip region 195Aand second extension region 225A includes at least portions of thosepatterns from the portion of first peripheral kerf 165A that overlapaxis 200A.

Third, first extension region 215B includes at least portions of thosepatterns from adjacent regions of fourth partial chip region 195D(rather than first region 195A) that extend into first partial chipregion 195A and second extension region 225B includes at least portionsof those patterns from the portion of first peripheral kerf 165A thatoverlap axis 200C.

Fourth, third clear bar 125C contains a third partial printable copyregion 205C. Third partial printable copy region 205C includes a thirdpartial chip copy region 210C which includes all the patterns of thirdpartial chip region 195C, a first extension region 215C1 which includesat least portions of those patterns from adjacent regions of firstpartial chip region 195A that extend into third partial chip region195C, a second extension region 215C2 which includes at least portionsof those patterns from adjacent regions of fourth partial chip region195D that extend into third partial chip region 195C, a third extensionregion 225C1 which includes at least portions of those patterns from theportion of first peripheral kerf 165A that overlap axis 200A, and afourth extension region 225C2 which includes at least portions of thosepatterns from the portion of first peripheral kerf 165A that overlapaxis 200B.

Fifth, fourth clear bar 125D contains a fourth partial printable copyregion 205D. Fourth partial printable copy region 205DC includes afourth partial chip copy region 210D which includes all the patterns offourth partial chip region 195D, a first extension region 215D1 whichincludes at least portions of those patterns from adjacent regions ofsecond partial chip region 195B that extend into fourth partial chipregion 195D, a second extension region 215D2 which includes at leastportions of those patterns from adjacent regions of third partial chipregion 195C that extend into fourth partial chip region 195D, a thirdextension region 225D1 which includes at least portions of thosepatterns from the portion of second peripheral kerf 165A that overlapaxis 200C, and a fourth extension region 225D2 which includes at leastportions of those patterns from the portion of first peripheral kerf165A that overlap axis 200C.

It should be noted that in the fifth embodiment of the present inventionin particular but in all embodiments in general, copy regions of cellregions need not be disposed parallel to the cell regions they arecopies of but may be rotated 90° from the cell regions they are copiesof.

The fourth and fifth embodiments of the present invention may beextended to include photomasks having multiple chip regions that are notidentical. In this case, different partial chip regions would includedifferent chip regions, portions of different chip regions orcombinations thereof.

Machine defect inspection tools that can perform the various scan, datastore, data compare and display steps illustrated in FIG. 6 anddescribed infra are well known in the art. There are two main types ofsuch inspection tools. In a first type, two different regions of thephotomask are scanned simultaneously through two lenses and the twoimages scanned are converted to digital data and compared almostimmediately. While there is “data stored: in this type of tool it isrelatively minimal. In a second type, a first region is scanned, theimages converted to digital data as the scan progresses and the digitaldata stored. Then a second region is scanned, the images converted todigital data as the scan progresses and the digital data stored. Thestored images can then be compared. The second type of tool can alsocompare scanned images to stored data.

FIG. 6 is a flowchart illustrating a method of inspecting a photomaskaccording to the present invention. In FIG. 6, an inspection tool of thesecond type as described supra is assumed. In step 300 a photomaskaccording to the present invention is loaded into a mask inspectiontool. In step 305, it is determined if the cell region of the photomaskhas multiple identical chip regions.

If there are multiple identical chip regions then, in step 310, eachchip region is scanned and the chip region image scan data is stored. Inone examples, scanning is performed by stepping a field of view across achip in a serpentine pattern, each step comprising a frame of image scandata, each frame of image scan data comprising a three dimensionalmatrix where the X and Y axis are pixel locations and the Z axis ispixel optical density. Generally, the chip region image scan data isstored as an individual chip region is scanned and the process of scanand store repeated for each chip region. In step 315, the image scandata for all chip regions are compared to one another and differences inthe data (exceeding a predetermined threshold difference) for the samearea of each chip region noted as potential defects and in step 320, thelocation or chip region X-Y coordinates of the potential defects isdetermined. In some machines, the operations of steps 310 and 315 areperformed sequentially on sub-regions of each chip region and only theimage scan data where potential defects have been detected is stored.

Next, in step 325, the potential defects are verified. When there areonly two chip regions, the potential defect location in both chipregions is displayed and a human operator can determine which chipregion is defective. When there are three or more chip regions only thenon-matching regions (assuming all but one match) potential defectlocations need be displayed and the human operator need only determineif an actual defect exist. However, all potential defect locations ofall chip regions may be inspected. The locations of actual chip regiondefects on the photomask are noted for potential repair operations.

Next, in step 330, each kerf copy region is scanned and the kerf copyimage scan data is stored. Then, in step 335, each kerf region isscanned and the kerf region image scan data stored. Since kerf copyregions include extension regions containing shapes that extend intoadjacent kerf regions as described supra, corresponding extensionregions of adjacent kerf regions are scanned as each kerf region isscanned. In step 340, the image scan data for each kerf region iscompared to the image scan data for its corresponding kerf copy regionand differences in the data (exceeding a predetermined thresholddifference) for the corresponding areas of kerf region and kerf copyregion are noted as potential defects and, in step 345, the location orkerf and kerf copy region X-Y coordinates of the potential defects aredetermined. In some machines, the operations of steps 330, 335 and 345are performed sequentially on corresponding sub-regions of each kerf andcorresponding kerf copy region and only the image scan data wherepotential defects have been detected is stored.

In the case where first and second kerf copies of the same kerf exist,the image scan data of each kerf copy can be compared to image scan dataof the kerf. If a same potential defect location occurs in bothcomparisons there is a high probability that an actual defect exists inthat location in the kerf region. If a same potential defect locationdoes not occur in both comparisons then there is a high probability thatan actual defect exists in one of the kerf copy regions. A comparison offirst kerf copy image data to second kerf image data can conclusivelydetermine if a potential defect exists in the kerf region or one of thekerf copy regions.

Next in step 350, the potential defects are verified. When there is onlyone kerf copy region, the potential defect location in both the kerfregion and its corresponding kerf copy region are displayed and a humanoperator can determine which chip region is defective. When there aretwo or more kerf copy regions for a corresponding kerf region only thenon-matching region (if its in the kerf region of the cell region)potential defect location need be displayed and the human operator needonly determine if an actual defect exist. The locations of actual kerfregion defects on the photomask are noted for potential repairoperations. Inspection is complete.

Returning to step 300, if there is only one chip region or non-identicalchip regions then the method proceeds to step 355. Next, in step 355,each partial copy region is scanned and the partial printable copyregion image scan data is stored. Then in step 360 each partial chipregion is scanned and the partial chip region image scan data stored.Since each partial chip region includes extension regions containingshapes that extend into adjacent partial chip regions and portions ofkerf regions adjacent to the partial chip region and extension region asdescribed supra, corresponding extension regions of adjacent partialchip regions and portions of kerf regions adjacent to the partial chipregion and extension region are scanned as each partial chip region isscanned. In step 365, the image scan data for each partial chip regionis compared to the image scan data for its corresponding partial copyregion and differences in the data (exceeding a predetermined thresholddifference) for the corresponding areas of partial chip region andpartial copy region are noted as potential defects and, in step 370, thelocation of partial chip region and partial copy region X-Y coordinatesof the potential defects are determined. In some machines, theoperations of steps 355, 360 and 365 are performed sequentially oncorresponding sub-regions of each partial chip region and correspondingpartial printable copy regions and only the image scan data wherepotential defects have been detected is stored.

Next, in step 375, the potential defects are verified. The potentialdefect location in both the partial chip region and correspondingadjacent kerf region and its corresponding partial copy region aredisplayed and a human operator can determine which chip region isdefective. The locations of actual partial chip region defects on thephotomask are noted for potential repair operations. Inspection iscomplete.

One of ordinary skill in the art would know the invention is applicablewhen an inspection tool of the first type is used, by essentiallyrealizing, that with minimal amounts of data storage, steps 310 and 315are looped, that steps 335 and 340 looped, and that steps 355, 360 and365 are looped in order to compare regions larger than the field of viewof the inspection tool.

FIG. 7 is a flowchart of a method of designing a photomask according tothe present invention. In step 400A, a chip graphic design system (GDS)dataset (also know as a shapes file) 405A is post processed to addvarious process and tool compensation to each shape in the GDS dataset405A to create a post-processed chip dataset 410A. Examples of postprocessing include optical proximity correction (OPC), process windowbias, and NFET/PFET length/width compensation. In step 415A it isdetermined if a copy of the chip(s) or portions of the chip are requiredfor writing to the clear bars of the photomask. If copies are required,then in step 420A, it is determined which portion of the chip(s) are tobe copied and in step 425A, the portions to be copied are broken intoparts that will fit into the area of the clear bars and still allow fora clear region between the copy and the frame, at least on the side ofthe copy adjacent to the cell region. Next, in step 430A, a chip copydataset 435A is created and, in step 440A, a chip copy layout file 445Ais generated. A chip copy layout file indicates where the chip copy isto be written on the photomask (it will be in a clear bar). The methodproceeds to step 450. Returning to step 415A, if no chip copies arerequired the method proceeds to step 450.

In step 400B, a kerf graphic design system (GDS) dataset (also know as ashapes file) 405B is post processed to add various process and toolcompensation to each shape in the GDS dataset 405B to create apost-processed kerf dataset 410B. Examples of post processing were givensupra. In step 415B it is determined if a copy of the kerf(s) orportions of the kerf are required for writing to the clear bars of thephotomask. If copies are required, then in step 420B, it is determinedwhich portion of the kerf(s) are to be copied and in step 425B, theportions to be copied are broken into parts that will fit into the areaof the clear bars and still allow for a clear region between the copyand the frame, at least on the side of the copy adjacent to the cellregion. Next, in step 430B, a kerf copy dataset 435B is created and, instep 440B, a kerf copy layout file 445B is generated. A kerf copy layoutfile indicates where the kerf copy is to be written on the photomask (itwill be in a clear bar). The method proceeds to step 450. Returning tostep 415B, if no kerf copies are required the method proceeds to step450.

In step 450, a photomask dataset (not shown) is generated from chipdataset 410A, chip copy dataset 435A (if it exists), chip copy layoutfile 445A (if it exists), a chip layout file 460A, kerf dataset 410B,kerf copy dataset 43 5B (if it exists), kerf copy layout file 445B (ifit exists), a kerf layout file 460B and a clear bar dataset and locationfile 465. Clear bar dataset and location file 465 indicates the size andlocation of the clear bars. Step 455 particularly merges kerf copy andchip copy datasets 435A and 435B with clear bar dataset and locationfile 465. Alternatively, the individual chip, chip copy, chip layout,kerf, kerf copy, kerf layout files and datasets and the clear bardataset and location file may be considered parts of a larger photomaskdataset.

Next, a photomask write dataset 455 is generated by converting thephotomask dataset into instructions that can be used to drive a directwrite tool (for example, an e-beam tool) used to fabricate a photomask .The opaque frame is defined by default, in that no dataset/location filegenerates patterns in the frame region outside of the clear bar regionswithin the frame region.

Generally, the method described herein with respect to designing aphotomask according to the present invention is practiced with ageneral-purpose computer and the method may be coded as a set ofinstructions on removable or hard media for use by the general-purposecomputer. FIG. 8 is a schematic block diagram of a general-purposecomputer for use in designing a photomask according to the presentinvention. In FIG. 8, computer system 500 has at least onemicroprocessor or central processing unit (CPU) 505. CPU 505 isinterconnected via a system bus 510 to a random access memory (RAM) 515,a read-only memory (ROM) 520, an input/output (I/O) adapter 525 for aconnecting a removable data and/or program storage device 530 and a massdata and/or program storage device 535, a user interface adapter 540 forconnecting a keyboard 545 and a mouse 550, a port adapter 555 forconnecting a data port 560 and a display adapter 565 for connecting adisplay device 570.

ROM 520 contains the basic operating system for computer system 500. Theoperating system may alternatively reside in RAM 515 or elsewhere as isknown in the art. Examples of removable data and/or program storagedevice 530 include magnetic media such as floppy drives and tape drivesand optical media such as CD ROM drives. Examples of mass data and/orprogram storage device 535 include hard disk drives and non-volatilememory such as flash memory. In addition to keyboard 545 and mouse 550,other user input devices such as trackballs, writing tablets, pressurepads, microphones, light pens and position-sensing screen displays maybe connected to user interface 540. Examples of display devices includecathode-ray tubes (CRT) and liquid crystal displays (LCD).

Thus, the present invention provides a single machine methodology forinspecting photomasks having regions that repeat and regions that do notrepeat.

A computer program with an appropriate application interface may becreated by one of skill in the art and stored on the system or a dataand/or program storage device to simplify the practicing the photomaskdesign portion of this invention. In operation, information for or thecomputer program created to run the photomask design portion of presentinvention is loaded on the appropriate removable data and/or programstorage device 530, fed through data port 560 or typed in using keyboard545.

The description of the embodiments of the present invention is givenabove for the understanding of the present invention. It will beunderstood that the invention is not limited to the particularembodiments described herein, but is capable of various modifications,rearrangements and substitutions as will now become apparent to thoseskilled in the art without departing from the scope of the invention.Therefore, it is intended that the following claims cover all suchmodifications and changes as fall within the true spirit and scope ofthe invention.

1. A photomask, comprising: a cell region, said cell region comprisingone or more chip regions, each chip region comprising a pattern ofopaque and clear sub-regions corresponding to features of an integratedcircuit chip and one or more kerf regions, each kerf region comprising apattern of opaque and clear sub-regions corresponding to features of anintegrated circuit kerf; a clear region formed adjacent to a side of acopy region, said copy region comprising opaque and clear sub-regionsthat are copies of at least a part of said cell region; and an opaqueregion between said clear region and said cell region.
 2. The photomaskof claim 1, wherein said copy region comprises a copy of all or lessthan a whole portion of a chip region of said one or more chip regions.3. The photomask of claim 1, wherein said copy region comprises a copyof all or less than a whole portion of a kerf region of said one or morekerf regions.
 4. The photomask of claim 3, wherein said clear regionfurther includes an additional copy region, said additional copy regioncomprising an additional copy of said all or less than a whole portionof said kerf region of said one or more kerf regions.
 5. The photomaskof claim 1, wherein said copy region comprises a copy of all or lessthan a whole portion of a kerf region of said one or more kerf regionsand a copy of all or less than a whole portion of a chip region of saidone or more chip regions.
 6. The photomask of claim 1, wherein saidclear region completely surrounds said copy region.
 7. The photomask ofclaim 1, wherein said opaque region completely surrounds said cellregion.
 8. The photomask of claim 6, wherein said opaque regioncompletely surrounds said cell region and said clear region.
 9. Thephotomask of claim 1, wherein said cell region has first, second, thirdand fourth sides, said first side opposite said second side, said thirdside opposite said fourth side, said clear region having a side adjacentand parallel to said first side of said cell region.
 10. The photomaskof claim 9, further including a second clear region having a sideadjacent and parallel to said second side of said cell region, a thirdclear region having a side adjacent to and parallel to said third sideof said cell region and a fourth clear region having a side adjacent andparallel to said fourth side of said cell region.
 11. The photomask ofclaim 10, further including additional copy regions comprising opaqueand clear sub-regions that are copies of at least additional parts ofsaid chip region, said additional copy regions disposed within one ormore of said second, third and fourth clear regions.
 12. The photomaskof claim 1, wherein said cell region has a first side and an oppositesecond side, said first and second sides each having a same firstlength, and a third side and an opposite fourth side, said third andfourth sides each having a same second length; wherein said clear regionhas a first side having a third length, said first side of said clearregion adjacent and parallel to said first side of said cell region; andwherein said third length is greater than said second length.
 13. Amethod of designing a photomask, comprising: generating a chip datasetrepresenting an integrated circuit chip design to be included in a cellregion of said photomask; generating a kerf dataset representing a kerfdesign to be included in said cell region; determining a portion of saidkerf dataset to copy; generating a kerf copy dataset, said kerf copydataset including said portion of said kerf dataset to copy; mergingsaid chip dataset, said kerf dataset and said kerf copy dataset into aphotomask dataset representing a pattern of clear and opaque regions ofsaid photomask.
 14. The method of claim 13, wherein said merging placesa pattern of clear and opaque regions defined by said chip dataset andby said kerf dataset in said cell region of said photomask and furtherplaces a pattern of clear and opaque regions defined by said kerf copydataset in clear bar regions of said photomask.
 15. The method of claim13, further including generating a write file containing codedinstructions for controlling operation of a tool for transferring saidphotomask dataset representing said pattern of clear and opaque regionsonto a blank mask substrate of a photomask fabrication line.
 16. Themethod of claim 13, further including: prior to said merging,determining a portion of said chip dataset to copy and generating a chipcopy dataset, said chip copy dataset including said portion of said chipdataset to copy; and said merging also including merging said chip copydataset into said photomask dataset.
 17. The method of claim 16, whereinsaid merging also places a pattern of opaque and clear regions definedby said chip copy dataset in said clear bar regions of said photomask.18. The method of claim 16, further including generating a write filecontaining coded instructions for controlling operation of a tool fortransferring said photomask dataset representing said pattern of clearand opaque regions onto a blank mask substrate of a photomaskfabrication line.
 19. A computer system comprising a processor, anaddress/data bus coupled to said processor, and a computer-readablememory unit coupled to communicate with said processor, said memory unitcontaining instructions that when executed implement a method for methodof designing a photomask, said method comprising the computerimplemented steps of: generating a chip dataset representing anintegrated circuit chip design to be included in a cell region of saidphotomask; generating a kerf dataset representing a kerf design to beincluded in said cell region; determining a portion of said kerf datasetto copy; generating a kerf copy dataset, said kerf copy datasetincluding said portion of said kerf dataset to copy; merging said chipdataset, said kerf dataset and said kerf copy dataset into a photomaskdataset representing a pattern of clear and opaque regions of saidphotomask.
 20. The computer system of claim 19, wherein said mergingplaces a pattern of clear and opaque regions defined by said chipdataset and by said kerf dataset in said cell region of said photomaskand further places a pattern of clear and opaque regions defined by saidkerf copy dataset in clear bar regions of said photomask.
 21. Thecomputer system of claim 19, wherein said method further includesgenerating a write file containing coded instructions for controllingoperation of a tool for transferring said photomask dataset representingsaid pattern of clear and opaque regions onto a blank mask substrate ofa photomask fabrication line.
 22. The computer system of claim 19, saidmethod further including: prior to said merging, determining a portionof said chip dataset to copy and generating a chip copy dataset, saidchip copy dataset including said portion of said chip dataset to copy;and said merging also including merging said chip copy dataset into saidphotomask dataset.
 23. The computer system of claim 22, wherein saidmerging also places a pattern of opaque and clear regions defined bysaid chip copy dataset in said clear bar regions of said photomask. 24.The computer system of claim 22, said method further includinggenerating a write file containing coded instructions for controllingoperation of a tool for transferring said photomask dataset representingsaid pattern of clear and opaque regions onto a blank mask substrate ofa photomask fabrication line.
 25. A method of fabricating a photomask,comprising: providing a transparent substrate having an opaque coating;forming a cell region by removing first areas of said opaque coating,said cell region comprising one or more chip regions and one or morekerf regions; forming a copy region by removing second areas of saidopaque coating, said copy region comprising a copy of a part of saidcell region; forming a clear region by completely removing third areasof said opaque coating; and wherein said clear region is formed betweena side of said substrate and a side of said cell region and separatedfrom said cell region by an opaque region and wherein a sub-region ofsaid clear region separates said copy region from said opaque region.26. The method of claim 25, wherein said part of said cell regioncomprises all or less than a whole portion of a kerf region of said oneor more kerf regions.
 27. The method of claim 25, wherein said part ofsaid cell region comprises all or less than a whole portion of a chipregion of said one or more patterned chip regions.
 28. The method ofclaim 25, further including forming an additional copy region byremoving additional second areas of said opaque coating, said additionalcopy region comprising a copy of at least an additional part of saidcell region different from said part of said cell region and wherein anadditional sub-region of said clear region separates said additionalcopy region from said copy region and from said opaque region.
 29. Themethod of claim 28, wherein said part of said cell region comprises allor less than a whole portion of a kerf region of said one or more kerfregions and said additional copy region comprises all or less than awhole portion of a different kerf region of said one or more kerfregions than comprised by said copy region.
 30. The method of claim 25,wherein said clear region further includes an additional copy region,said additional copy region also comprising said copy of at least saidpart of said cell region.
 31. The method of claim 30, wherein said partof said cell region comprises all or less than a whole portion of a kerfregion of said one or more kerf regions and said additional copy regioncomprises all or less than a whole portion of said kerf region of saidone or more kerf regions.
 32. The method of claim 25, wherein said partof said cell region comprises all or less than a whole portion of a kerfregion of said one or more kerf regions and all or less than a wholeportion of a chip region of said one or more chip regions.